Silane-functionalized ultraviolet screen precursors

ABSTRACT

Silane-functionalized ultraviolet screening agent precursors comprise compounds of the formula: ##STR1## wherein R is ##STR2## R 1  is C 1  -C 6  alkyl, R 2  is C 1  -C 6  alkyl or C 2  -C 6  alkanoyl, R 3  is hydrogen or C 1  -C 6  alkoxyl, X is 0,1 or 2, y is 1,2, or 3 and x+y=3. Under ultraviolet radiation the compounds rearrange to the corresponding α-hydroxybenzophenones which protect substrates, especially transparent plastics, against degradation.

This invention relates to precursors for ultraviolet screening agents.More particularly, it relates to silane-functionalized-phenyl benzoatesand -phenyl phenylsulfonates. It is also concerned with ultravioletcurable coating compositions containing the precursors, and tosubstrates coated with such cured compositions.

BACKGROUND OF THE INVENTION

Many thermoplastics, such as LEXAN® polycarbonate, require mar-resistantsurface coatings to retain transparency under normal operatingconditions when used as glazing materials in buildings and in railroadcars, airplanes and the like. A particularly useful family of suchcoatings are mixtures of silica and hydrolyzable silanes in a hydrolysismedium, such as alcohol and water, see, for example, Misch et al., U.S.Pat. No. 3,708,225; Clark, U.S. Pat. No. 3,986,997 and 3,976,497; andUbersax, U.S. Pat. No. 4,177,315, as well as in copending applicationSer. No. 964,910, filed Nov. 30, 1978. Such coatings are curedthermally, and ultraviolet resistance can be imparted by incorporating avariety of known phenolic ultraviolet (uv) screening agents. These tendto migrate or exhibit plasticizing effects, however, so thatsilane-functionalization of uv screens, e.g., by forming silylalkylether substituents has been developed to insure reaction into thecoating composition.

See U.S. Pat. No. 4,278,804 (Ashby et al.); U.S. application Ser. No.154,621 (Ashby), now allowed, filed May 30, 1980; copending U.S.application Ser. No. 154,625 (Ching), filed May 30, 1980; and U.S.application Ser. No. 154,626 (Ching), now allowed, filed May 30, 1980.

A somewhat more recent development in surface coatings is described inthe copending application of Chung, U.S. Ser. No. 129,297, filed Mar.11, 1980, disclosing ultraviolet light curable silicone hard coatingcompositions. The various known uv screeners are not effective for suchcompositions because they retard the curing needed for producing thehardened surface. The foregoing patents and applications areincorporated herein by reference.

It has now been found that functionalized derivatives of precursors ofuv screens can be provided, and these will overcome the retardation ofuv-curable compositions of the type described in the Chung application.It is further observed that after completion of uv-curing, theprecursors will then generate a functionalized uv screen in situ by aphotoreaction which is known as a Fries rearrangement. By way ofillustration, compound 1 will rearrange to uv-screen 2 as follows:##STR3##

Entirely analogous to this, the precursors contemplated by thisinvention, as particularly to be described, will undergo a Friesrearrangement to produce hydroxybenzophenone and hydroxyphenylphenylsulfonyl uv screens which effectively protect, e.g.,poly(bisphenol A carbonate) from yellowing under silicone uv-cured hardcoats.

Description of the Invention

According to the present invention, there are providedsilane-functionalized ultraviolet screening agent precursors selectedfrom compounds of the formulae: ##STR4## R¹ is C₁ -C₆ alkyl, R² is R² isC₁ -C₆ alkyl or C₂ -C₅ alkanoyl, R³ is hydrogen or C₁ -C₆ alkoxyl, x is0,1 or 2, y is 1, 2 or 3, and x+y=3.

In preferred embodiments of compound (i), R is ##STR5## R¹ and R² areCH₃, R³ is OCH₃, x is l and y is z; in compound (ii), R is ##STR6## R²is --CH₃ or --CH₂ CH₃, R³ is H, x is 0 and y is 3; in compound (iii) Ris ##STR7## R² is CH₃ or --CH₂ CH₃, x is 0 amd y is 3.

The compounds can be used as ultraviolet screening agent precursors inplastics or in coatings, and the like. In preferred embodiments,however, they will be used in coating compositions comprising a mixtureof ingredient (A) which is the acid hydrolysis product of analkoxy-functional silane and ingredient (B) which is the acid hydrolysisproduct of an acryloxy-functional silane or the acid hydrolysis productof a glycidoxy-functional silane, or mixtures thereof. In the mixture isa catalytic amount of a cationic photoinitiator which is effective forfacilitating the ultraviolet cure reaction of the hydrolysis products.Illustrative photoinitiators can be radiation-sensitive halonium,phosphonium or sulfonium salts.

Among the embodiments of the invention, therefore, are radiation curablecoating compositions comprising

(A) 100 parts by weight of an acid hydrolysis product of analkoxy-functional silane;

(B) 10 to 1000 parts by weight of

(i) an acryloxy-functional silane;

(ii) a glycidoxy-functional silane; or

(iii) a mixture of (i) and (ii);

(C) a catalytic amount of a photoinitiator; and

(D) from 2 to 15 parts by weight of a silane-functionalized ultravioletagent precursor compound as defined above.

The invention also contemplates substrates coated with such compositionsand cured by uv light to provide a hard coating containing the uv screengenerated in situ therein.

The compounds of this invention can be made in a number of ways.

Compound (i) is accessible by reacting eugenol, a commercially availablematerial, with benzoyl chloride or benzenesulfonyl chloride, and thenadding a hydrosilane across the double bond using a platinum catalystaccording to the following pathway: ##STR8## wherein R, R¹, R², x and yare as defined above.

Compound (ii) is accessible by reacting resorcinol with allyl bromide,then with benzoyl chloride or benzenesulfonyl chloride, and finallyadding a hydrosilane across the double bond using a platinum catalystaccording to the following pathway: ##STR9## wherein R, R¹, R², x and yare as defined above.

Compound (iii) is accessible by reacting the corresponding substitutedphenybenzotriazole with allyl bromide and then with benzoyl chloride orbenzenesulfonyl chloride and finally adding a hydrosilane across thedouble bond using a platinum catalyst according to the followingpathway: ##STR10## wherein R, R¹, R², x and y are as above-defined.

Examples illustrating the preparation of these embodiments are set forthhereinafter.

With respect to the coating compositions employed in the presentinvention, one of the major constituents is ingredient (A) which is thehydrolysis product of alkoxy-functional silane. Such a silane willordinarily have the following general formula:

    R.sub.a.sup.4 --Si--(OR.sup.5).sub.4-a

wherein R⁴ and R⁵ are the same or different monovalent hydrocarbonradicals, including halogenated species of such radicals. Preferably, R⁴and R⁵ will be lower alkyl, e.g., C₁ -C₆, radicals such as methyl,ethyl, propyl, etc., but may include other saturated and unsaturatedspecies including vinyl, aryl, etc. The letter a is an integer from 0 to3 such that there are 4-a alkoxy groups in the silane molecule. Sincetetra-alkoxy silanes are particularly effective, a will often equalzero.

The hydrolysis product of such silanes is obtained by contacting thesilanes with an excess of water in the presence of a catalytic amount ofacid. When less than a stoichiometric amount of water is utilized, apartial-hydrolyzate is obtained. Such partial-hydrolyzates can also beused to obtain the hard coatings of the present invention. Among theparticularly useful alkoxy-functional silanes are the following:tetraethoxysilane, ethyltriethoxysilane, diethyldiethoxysilane,triethylethoxysilane, tetramethoxysilane, methyltrimethoxysilane,dimethyldimethoxysilane, and trimethylmethoxysilane.

The second major ingredient is ingredient (B) which is the acidhydrolysis product of an acryloxy-functional silane or the acidhydrolysis product of a glycidoxy-functional silane or mixtures thereof.The acryloxy-functional silane has a general formula given by (II).##STR11## wherein R⁶ and R⁷ are the same or different monovalenthydrocarbon radicals as described above for R⁴ and R⁵. R⁸ is a divalenthydrocarbon radical having from 2 to 8 carbon atoms. R⁹ is a hydrogen ora monovalent hydrocarbon radical. The letter b is an integer from 1 to3, c is an integer from 0 to 2 and d is an integer equaling 4-b-c. Inmany of the embodiments of the present invention, b will ordinarily be3, c will be 0 and d will equal 1. Specific examples ofacryloxy-functional silanes include:

3-methacryloxypropyltrimethoxysilane

3-acryloxypropyltrimethoxysilane

2-methacryloxyethyltrimethoxysilane

2-acryloxyethyltrimethoxysilane

3-methacryloxypropyltrimethoxysilane

3-acryloxypropyltriethoxysilane

2-methacryloxyethyltriethoxysilane

2-acryloxyethyltriethoxysilane

Such acryloxy-functional silanes are commercially available. Forexample, 3-methacryloxypropyltrimethoxysilane can be obtained from UnionCarbide. The second major constituent (Ingredient B) of the coatingcomposition may also be a glycidoxy-functional silane instead of theacryloxy-functional silane just described, or it may be a combination ormixture of both types of silane. A glycidoxy-functional silane has thegeneral formula given by (III). ##STR12## wherein R¹⁰ and R¹¹ are thesame or different monovalent hydrocarbon radicals as described above forR⁴ and R⁵. R¹² is a divalent hydrocarbon radical having from 2 to 8carbon atoms. The letter e is an integer from 1 to 3, f is an integerfrom 0 to 2 and g is an integer equaling 4-e-f. Specific examples ofuseful glycidoxy-functional silanes are the following:

3-glycidoxypropyltrimethoxysilane

3-glycidoxyethyltrimethoxysilane

3-glycidoxypropyltriethoxysilane

3-glycidoxyethyltriethoxysilane

These glycidoxy-functional silanes are also commercially available. Onesource, for example, is Petrarch Systems, Inc. The ultraviolet radiationcurable coating composition of the present invention will be comprisedof 100 parts by weight of the acid hydrolysis product of thealkoxy-functional silane given by formula I which is combined with fromapproximately 10 to 1000 parts by weight of either the acid hydrolysisproduct of the acryloxy-functional silane given by formula II or theglycidoxy-functional silane given by formula III, or combinationsthereof. To this mixture must be added a catalytic amount of a cationicphotoinitiator and from 2 to 15 parts by weight of the ultraviolet agentprecursor compound. Effective photoinitiators are radiation sensitivearomatic halonium, sulfonium or phosphonium salts which have beendescribed in the literature.

Cationic photoinitiators have been described by Crivello in numerousU.S. patents and applications, such as the following, for example, whichare hereby incorporated by reference: U.S. Pat. Nos. 4,136,102 issuedJan. 23, 1979 and 3,981,897 issued Sept. 21, 1976. Such cationicphotoinitiators can have the general formula given by (IV).

    [R.sup.13 --C.sub.6 H.sub.4 ].sub.n X.sup.+ [MQ.sub.h ].sup.-(IV)

In this formula, X is a radical selected from I, P or S. M is a metal ormetalloid and Q is a halogen radical selected from Cl, F, Br, or I. R¹³is hydrogen or a monovalent hydrocarbon radical having from 1 to 12carbon atoms. The letter h is an integer having the value of 4 to 6inclusive, an n is an integer having the value of 2 or 3.

The expression [MQ_(h) ]⁻ applies to any number of ionic species butpreferably will be selected from SbF₆ ⁻, AsF₆, BF₄ ⁻ and PF₆ ⁻.

It is ordinarily preferably to utilize approximately 0.20 parts byweight of the cationic photoinitiator for every 100 parts by weight ofthe mixture of ingredients A and B as described above. However,depending upon individual desired process parameters such as rate ofcure and ultimate abrasion-resistance, the amount of the photoinitiatorcan range from approximately 0.01 to 5 parts by weight per 100 parts ofthe mixture of ingredient A and B.

The cationic photoinitiators are particularly effective for initiating across-linking reaction between the hydrolyzed alkoxy groups of thecompositions given by formulas I, II, and III upon exposure toultraviolet radiation. Good hard coatings having excellent adhesion canthus be obtained when the coating composition is applied to a substrateand exposed to radiation such as that provided by UV lamps.

The UV-curable coating composition of the present invention isordinarily coated on at least one surface of some solid substrate. Thesolid substrate may be comprised of a synthetic organic polymer or ametal or even glass. Also included are synthetic organic polymersubstrates which themselves have a metallized surface.

Prior to the composition being coated upon a substrate there mayoptionally be included a priming step wherein a primer such as athermosetting acrylic emulsion could first be applied to the substrate.After the coating composition is applied to the substrate or the primedsubstrate, the coating may be cured thereon and the uv screen generatedin situ by exposure to an effective amount of UV-radiation, which may beobtained from, for example, a Hanovia 550 watt lamp or a PPG Processor,Model QC1202.

The coating compositions of the present invention can be applied to avariety of solid substrates by conventional methods, such as flowing,spraying or dipping, to form a continuous surface film. Optimum coatingthicknesses are obtained by slow dip coating procedures. Substrateswhich are especially contemplated herein are transparent andnon-transparent plastics and metals. More particularly, these plasticsare synthetic organic polymeric substrates such as acrylic polymers likepoly-(methylmethacrylate), polyesters, such as poly(ethyleneterephthalate), poly(butylene terephthalate), etc., polyamides,polyimides, acrylonitrile-styrene copolymers,styrene-acrylonitrile-butadiene copolymers, polyvinyl chloride,butyrates, polyethylene and the like. The coating compositions of thisinvention are especially useful as coatings for polycarbonates, such aspoly(bisphenol-A carbonate) and those polycarbonates known as Lexan®,sold by General Electric Company, and as coatings for injection moldedor extruded acrylics, such as polymethylmethacrylates. Metal substrateson which the present protective coatings are also effective includebright and dull metals like aluminum and bright metallized surfaces likesputtered chromium alloy. Other solid substrates contemplated hereininclude wood, painted surfaces, leather, glass, ceramics and textiles.

By choice of the proper formulation, application conditions andpretreatment of the substrate including the use of primers, the coatingscan be adhered to substantially all solid substrates. A hard coatinghaving all of the aforementioned characteristics and advantages isobtained by the removal of any residual solvent and volatile materialssuch as methanol or ethanol byproducts of the hydrolysis reactions. Notethat except for such residual moieties the present invention providesessentially solventless coating compositions.

Coating thicknesses may vary but for improved abrasion-resistancecoating thicknesses of 3-10 microns and preferably 5 microns, areutilized.

In order that those skilled in the art may better understand how topractice the present invention, the following examples are given by wayof illustration and not by way of limitation.

EXAMPLE 1 (a) 2-Methoxy-4-allylphenyl benzoate

A mixture of 1 mole of 1-allyl-3-hydroxy-4-methoxybenzene (eugenol), 1mole of potassium hydroxide and one mole of benzoyl chloride in water isstirred at 18°-20° C. for 12 hours under nitrogen. The resulting solidis filtered off and washed with water. Recrystallization fromisopropanol yields 2-methoxy-4-allylphenyl benzoate, m.p., 64°-65° C.

(b) 2-Methoxy-4-methyldimethoxysilylpropylphenyl benzoate

To a solution of 1 mole of 2-methoxy-4-allylphenyl benzoate in tolueneis added 2 moles of methyldimethoxysilane at 18°-20° C. in the presenceof a catalytic amount of a platinum-hydrosilation complex (GE'sSPBD-88034). The reaction mixture is evaporated until solvent-free,leaving the product as a pale yellow oil.

The procedure is repeated substituting benzenesulfonyl chloride forbenzoyl chloride in step (a) and there is obtained2-methoxy-4-methyldimethoxysilylpropylphenyl benzenesulfonate.

EXAMPLE 2 (a) 3-Allyloxyphenyl benzoate

In a one-liter, three-necked flask equipped with a thermometer, refluxcondenser, dropping funnel, heating mantle and mechanical stirrer areplaced 107 g. (0.5 mole) of resoscisol monobenzoate, 500 ml. of dryacetone, and 69 g. (0.5 mole) of potassium carbonate. Seventy-five grams(0.62 mole) of allyl bromide is then added slowly with stirring undernitrogen at about 20° C. After addition of allyl bromide is complete,the mixture is refluxed for 16 hours. The reaction mixture is cooled toabout 20° C. and concentrated under reduced pressure. Methylene chlorideis added, and washed with dilute sodium bicarbonate solution. Theorganic layer is dried over anhydrous magnesium sulfate and upon removalof the organic solvent, a light yellow liquid is obtained. The crudematerial is distilled at 145° C./0.03 mm Hg. to give 98 g. of product.

(b) 3-(3-Trimethoxysilylpropoxy)phenyl benzoate

A mixture of 25.4 g. (0.1 mole) of 3-allyloxyphenyl benzoate, 50 ml. ofdry toluene, 20 g. (0.15 mole) of trimethoxysilane and 2 drops ofplatinum hydrosilation catalyst is heated at 90° C. for 17 hours undernitrogen. After the reaction mixture is cooled to about 20° C., it isconcentrated under reduced pressure to produce the uv precursor product.For purification, the product is passed through a short silica columnusing dichloromethane as an eluent.

EXAMPLE 3 4-(3-Trimethoxysilylpropoxy)-2-(1-N-benzotriazolyl)phenylbenzoate

Following the same process of Example 2, step (b), the title compound isobtained from the reaction of 37.1 g. (0.1 mole) of4-allyloxy-2-(1-N-benzotriazolyl)phenyl benzoate, 25 g. (0.2 mole) oftrimethoxysilane, 100 ml. of dry toluene, and a catalytic amount of aplatinum hydrosilation catalyst.

EXAMPLE 4

A mixture of 52 grams (0.25 mole) of tetraethoxysilane (TES) and 9 grams(0.5 mole) of water is cooled to approximately 0° to 3° C., and 0.4grams of perchloric acid is added. The reaction mixture is stirred asthe ice melts away. After removal of some insoluble particles byfiltration, a clear solution of TES-hydrolyzate having a viscosity of5.6 centistokes is obtained. Next, a second emulsified solution isobtained by mixing 24.8 grams (0.1 mole) of3-methacryloxypropyltrimethoxysilane (MPTMS) and 2.7 grams (0.15 mole)of water to which 2 drops of perchloric acid are added at roomtemperature. After stirring overnight at room temperature, a pale,greenish solution of MPTMS-hydrolyzate is obtained having a viscosity of8.6 centistokes. Into a mixture of 5 grams of TES-hydrolyzate and 4grams of MPTMS-hydrolyzate is added 60 mg. of a cationic catalyst,diphenyliodoniumhexafluoroarsenate. Then, 1.0 grams of2-methoxy-4-methyldimethoxysilylpropylphenyl benzoate is added. A clearsolution is obtained which is flow coated upon a transparent sheet ofLexan®, poly(bisphenol A carbonate), and the coated panel is dried atroom temperature for 30 minutes. Then it is irradiated under a singleHanovia 550 watt lamp. A hard coating with good adhesion is obtainedwithin 12 to 60 seconds. The panel has excellent resistance to yellowingbecause uv exposure generates in situ the compound2-hydroxy-3-methoxy-5-methyldimethoxysilylpropylbenzophenone.

The procedure of Example 4 is repeated, substituting the uv screenprecursors of Examples 2 and 3, respectively. Again there are obtainedtransparent, hard coated poly(bisphenol A carbonate) sheets withexcellent resistance to yellowing.

Obviously, many variations will suggest themselves to those skilled inthis art in light of the above, detailed description. All suchmodifications are within the intended scope of the appended claims.

We claim:
 1. A silane-functionalized ultraviolet screening agentprecursor selected from compounds of the formulae: ##STR13## (iv) amixture of any of the foregoing, wherein R is ##STR14## R¹ is C₁ -C₆alkyl, R² is C₁ -C₆ alkyl or C₂ -C₅ alkanoyl, R³ is hydrogen or C₁ -C₆alkoxyl, x is 0, 1 or 2, y is 1, 2 or 3, and x+y=3.
 2. A compound asdefined in claim 1 which is of the formula: ##STR15##
 3. A compound asdefined in claim 1 which is of the formula: ##STR16## wherein R² is--CH₃, or --CH₂ CH₃.
 4. A compound as defined in claim 1 which is of theformula: ##STR17## wherein R² is --CH₃ or --CH₂ CH₃.